This invention relates to cement dispersion agents. Cement dispersion agents are used for cementing compositions such as mortar and concrete in order to provide them with fluidity and water reducing property. The present invention relates in particular to such cement dispersion agents that are capable of providing high fluidity to cementing compositions, restraining the change in fluidity such as slump loss with the passage of time after kneading, and reducing the drying shrinkage of hardened concrete which is obtained at the same time.
Although many kinds of natural and synthetic cement dispersion agents have been in use, most of them can provide only low fluidity to cementing compositions and their slump losses are large. There were proposals to use water-soluble vinyl copolymers as cement dispersion agent (Japanese Patent Publications Tokkai 62-78137 and Tokkai 1-226757, U.S. Pat. Nos. 4,962,173, 4,960,465 and 5,028,271). Although they can provide relatively high fluidity to cementing compositions and their slump losses are relatively small, their effects are still insufficient. In particular, they are not satisfactory in that the drying shrinkage of hardened concrete which is obtained is large and shrinkage cracks are formed in such hardened concrete as a result.